Many of today's intravascular endocardial leads are multipolar leads typically comprising a tip electrode and one or more ring electrodes disposed along the distal end of the lead body. The various electrodes transmit electrical stimulation pulses from an implantable medical device such as a pacemaker or implantable cardioverter defibrillator (ICD) to the tissue to be stimulated, and/or transmit naturally occurring sensed electrical signals from the tissue to the medical device. In a typical bipolar lead having a tip electrode and a ring electrode, two helically wound conductor coils with insulation in between are arranged coaxially and carried within a single lumen of the lead body. The inner conductor coil connects the medical device with the tip electrode while the outer conductor coil, somewhat shorter than the inner coil, connects the medical device with the ring electrode positioned proximally of the tip electrode.
To accommodate placement of multipolar leads into the coronary veins or permit their use with other leads (such as in four-chamber or whole heart pacing) it has become necessary to reduce the outside diameter of the leads. In one approach to accomplishing this goal, the various conductor coils, each individually insulated, are interleaved and wound about the same coil diameter instead of being arranged coaxially.
To further reduce the outside diameter of multipolar leads, lead bodies having multiple lumens have been developed. In place of helically wound coils, individually insulated, monofilament, non-coiled wire conductors or multifilar, braided cable conductors are used to connect the medical device with the electrodes along the distal end of the lead. Multilumen lead bodies may also carry defibrillation electrodes supplied by associated cable or wire conductors.
In one conventional cable or wire conductor lead design, individual, separately insulated conductors each occupy a separate lumen. In another design, multiple cable or wire conductors, each separately insulated, share a single lumen. In the first design, the number of cable or wire conductors that can be used is limited by the cross sectional area limitations of the lead body. In the second design, although multiple cable or wire conductors within a common lumen can allow for a smaller diameter lead, this design often entails inefficient, time-consuming individual conductor preparation and lead assembly, and may result in conductors being crossed during assembly.
Accordingly, despite significant advances made in the art, some of which have been summarized above, there continues to be a need for simpler, lower cost, smaller diameter, lead designs amenable to more efficient and reliable fabrication.